There is a demand for electronic equipments such as, for example, a cellular phone to have a housing of a waterproof structure. In order to make a waterproof housing, there is suggested the following methods.                1) A method to make a sealed structure by compressing a sealing material by two case parts facing each other.        2) A method to make a sealed structure by applying a sealant between two case parts.        3) A method to make a sealed structure by attaching two case parts to each other using a double-stick tape.        
In order to allow disassembling a housing (case) to repair or replace component parts inside the housing, the above-mentioned method 1) is suitable. According to the method 1), a seal material can be compressed to make a waterproof structure by fitting the seal material into a groove provided on one of the cases (a case body) and assembling the other case (a case lid) to the main case. The seal material is an elongated elastic material, which can provide a sealing function by being pressed by the main case and the case lid within the groove.
Here, there is suggested a waterproof structure with a seal material having a projection on a side surface thereof to maintain a waterproof property even if a water pressure changes (for example, refer to Japanese Laid-Open Patent Application No. 2008-218633). In this waterproof structure, a water pressure applied to a case acts as a force to further compress a seal material, and thereby a seal surface pressure can be increased as the water pressure is increased. Additionally, a waterproof property can be improved by improving a surface pressure of the projection formed on the side surface of the seal material by causing the seal material to be pressed toward inner side by a pressure of water entering through a gap between an upper case and a lower case. It should be noted that the same effect may be obtained by a seal material such as an O-ring having a cross section protruding in a side direction.
The above-mentioned sealed structures have the following problems.
1) A sealed structure in which a seal material is compressed between case parts facing each other.
An amount of compression of the seal material depends on assembly size dimensions, and, the amount of compression does not change even if a water pressure is applied to the sealed structure including the seal material. Therefore, even in a state where a case assembly is submerged, a repulsion force generated by the seal material and applied to the case assembly does not change. If an amount of compression of the seal material is increased to improve a seal property, there is a possibility that the case assembly is deformed, which results in the case assembly being opened.
In the waterproof structure disclosed in the above-mentioned Japanese Laid-Open Patent Application No. 2008-218633, the upper and lower case parts are assembled by being positioned to each other at a fitting position. Accordingly, even if a water pressure is increased, the compression of the seal material does not go beyond the compression by the upper and lower case parts at the fitting positions where the lower and upper case parts are assembled and fixed to each other. Moreover, although it is explained in the above-mentioned patent document that the seal material is displaced toward inside the case assembly in the retaining groove due to a water pressure exerted on the seal material, the seal material may be deformed but not displaced in the retaining groove toward inside the case assembly because a high surface pressure has already been generated due to compression by the upper and lower case parts and a friction is generated in the seal material, which is formed by a rubber-like elastic material.
2) A sealed structure using a seal agent.
A processing efficiency is not good because a manufacturing process cannot proceed to a subsequent process until the seal agent cures. Additionally, when disassembling the case assembly, the seal part is destroyed completely. Thus, the seal part must be removed completely if the case parts are reused. If the case parts are not reusable, the case parts are discarded, which generates a wasteful cost.
3) A seal structure using a double-stick tape.
Although a double-stick tape can be used to make a seal between flat surfaces, it is difficult to apply the double-stick tape to a three-dimensional surface. Additionally, if an adhesive of the double-stick tape remains on the case parts when the case assembly is disassembled, the remaining adhesive must be removed completely in order to reuse the case parts. If the remaining adhesive cannot be removed, the case parts must be discarded and use new case parts, which generates a wasteful cost.